1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method of transmitting and receiving Automatic Repeat reQuest (ARQ) feedback information in a wireless communication system.
2. Discussion of the Related Art
First, the format of a Medium Access Control (MAC) Protocol Data Unit (PDU) of the related art and the format of a generic MAC header will be described with reference to FIGS. 1 and 2.
FIG. 1 is a diagram showing the format of the MAC PDU of the related art and FIG. 2 is a diagram showing the format of the generic MAC header of the related art.
Referring to FIG. 1, the MAC PDU includes a generic MAC header, a payload and a Cyclic Redundancy Check (CRC).
The generic MAC header is a part in which control information is carried, the payload is a part in which actual information excluding a header for various operations and control is carried, and the CRC is a part in which a result extracted from data by a polynomial equation at a transmitter side is carried for error check.
Referring to FIG. 2, an HT field indicates a header type. The generic MAC header of the related art is roughly divided into two header types according to presence/absence of the payload, and the HT field indicates the header type of the generic MAC header. The value of the HT field is set to 0 if the generic MAC header has a payload and the value of the HT field is set to 1 if the generic MAC header does not have a payload.
The generic MAC header which does not have the payload is used for signaling information transmission, and examples of the type of the signaling header defined in the related art include a MAC signaling header type 1 and a MAC signaling header type 2. The MAC signaling header type 1 includes a bandwidth (BW) request, a bandwidth request and uplink transmission power report (BR and UL Tx power report), a carrier-to-interference-noise ratio (CINR) report, and a physical channel report, and the MAC signaling header type 2 includes a feedback header.
A Type field indicates whether or not MAC subheaders are transmitted. In the related art, six MAC subheaders are defined, and the Type field has 6 bits, each of which indicates whether or not each of the subheaders is present.
The six MAC subheaders defined in the related art include a Fragmentation Subheader (FSH), a Grant management Subheader (GMSH), a Packing Subheader (PSH), an Automatic Repeat reQuest (ARQ) feedback subheader, a Mesh subheader and a Fast-Feedback Allocation Subheader (FFSH).
Next, the FSH and the PSH will be described with reference to FIGS. 3 and 4.
FIG. 3 is a diagram showing a method of adding a FSH and a PSH in the case of ARQ-enabled connection.
As shown in FIG. 3, in the case where only a service Data Unit (SDU) which is not fragmented is transmitted or in the case where one fragment of the SDU is transmitted by fragmentation, the FSH is added in front of the SDU or the fragment of the SDU. In the case where SDU fragments generated from different SDUs of the same connection are transmitted together, the PSH is added in front of each of the SDUs or the fragments of the SDUs.
FIG. 4 is a diagram showing a method of adding a FSH and a PSH in the case of non-ARQ-enabled connection.
As shown in FIG. 4, no subheader is added in the case where only the SDU which is not fragmented is transmitted, and the FSH is added in front of the fragment of the SDU for packet reordering of a receiver if only one fragment of the SDU is transmitted by fragmentation. In the case where SDU fragments generated from different SDUs of the same connection are transmitted together, the PSH is added in front of each of the SDUs or the SDU fragments.
The FSH of the related art includes a 2-bit Fragmentation Control (FC) field indicating whether or not fragmentation is performed and an 11-bit Sequence Number (SN) field, and the PSH includes an FC field, an SC field and an 11-bit length (LEN) field.
Next, an ARQ feedback method of the related art will be described.
In the related art, when a receiver receives an ARQ-enabled PDU, the receiver transmits acknowledgement (ACK) or Negative Acknowledgement (NACK) through an ARQ feedback Information Element (IE). That is, the ACK or NACK of all transmitted ARQ-enabled PDUs is transmitted by the receiver according to ARQ feedback types. The ARQ feedback is transmitted in the payload format by the ARQ feedback IE, transmission of the ARQ feedback payload is indicated by a fourth bit of the Type field of the generic MAC header, and the ARQ feedback IE is located at a first location of packed SDUs or SDU fragments when being packed together with other MAC SDUs.
However, recently, according to an IEEE 802.16m system which is being standardized, a transmitter may transmit an ARQ feedback polling request to a receiver, and the receiver transmits an ARQ feedback to the transmitter if the ARQ feedback polling request is received from the transmitter or if an ARQ block is not received in a predetermined period.
Accordingly, there is a need for a method of, at a transmitter, transmitting an ARQ feedback polling request to a receiver and an ARQ feedback transmission indication method of indicating whether or not a receiver transmits an ARQ feedback to a transmitter.
As described above, according to the related art, an ARQ feedback polling request method and an ARQ feedback transmission indication method are not defined. However, according to the IEEE 802.16m system, there is a need for an ARQ feedback polling request method and an ARQ feedback transmission indication method.